Method of producing a flat top slab of foamed polyurethane

ABSTRACT

A method for the continuous production of slabs of polymeric foam. Slabs of foam are produced by depositing liquid foam reactants onto an open-topped continuous trough conveyor and a flat top surface on the foam is achieved by introducing guide sheets between the sides of the trough conveyor and the foam and raising and controlling the guide sheets so that they are always in accurate registration with the rising foam. The guide sheets are introduced downwardly into the trough conveyor and then passed around respective straight fold bars the attitudes of which are adjustable. The guide sheets thereafter follow upwardly-inclined paths, corresponding to the rising level of the foam, and are advanced by pull rolls which are also adjustable in attitude. The positions along the trough conveyor of the fold bars and the pull rolls can be adjusted. Preferably, the guide sheets are sheets of thin plastic material, e.g. polyethylene.

[111 3,812,227 [451 May 21,1974

1 1 METHOD OF PRODUCING A FLAT TOP SLAB OF FOAMED POLYURETHANE [76]Inventors: James Brian Blackwell; Dennis Killen; Victor Francisl-lodgson, all of Yew St., Stockport, England 22 Filed: Jan. 21, 1972[21] App]. No.: 219,645

Related US. Application Data [63] Continuation-impart of Ser. No.719,957, April 9,

1968, abandoned.

[30] Foreign Application Priority Data Dec. 13, 1967 Great Britain56752/67 June 9, 1967 Great Britain 26718/67 Apr. 12, 1967 Great Britain16670/67 [52] US. Cl 264/54, 264/40, 264/48, 264/55, 264/316, 425/4 C,425/145, 425/436 [51] Int. Cl 1329!! 27/04 [58] Field of Search 264/54,47, 51 48, 53, 264/40, 316, 425/140, 141, 436, 145, 327

[56] References Cited I UNITED STATES PATENTS 3,325,823 6/1967 Boon264/54 X 3,492,693 2/1970 Clarke et a1. 425/327 3,576,935 4/1971 Dyer etal. 264/95 3,639,550 2/1972 Darmochwal 264/54 X 3,719,234 3/1973Petzetakis 264/54 X 3,091,811 6/1963 Hackert 264/48 X 3,240,655 3/1966Voelker 264/47 X 3,233,576 2/1966 Voelker 264/47 X 3,655,311 4/1972Porter 264/47 X FOREIGN PATENTS OR APPLICATIONS 17,667 10/1966 Japan264/51 Primary Examiner-Philip E. Anderson Attorney, Agent, orFirm-Waters, Roditi, Schwartz & Nissen [5 7 ABSTRACT A method for thecontinuous production of slabs of polymeric foam. Slabs of foam areproduced by depositing liquid foam reactants onto an open-toppedcontinuous trough conveyor anda flat top surface on the foam is achievedby introducing guide sheets between the sides of the trough conveyor andthe foam and raising and controlling the guide sheets so that they arealways in accurate registration with the rising foam. The guide sheetsare introduced downwardly into the trough conveyor and then passedaround re spective straight fold bars the attitudes of which areadjustable. The guide sheets thereafter follow upwardly-inclined paths,corresponding to the rising level of the foam, and are advanced by pullrolls which are also adjustable inattitude. The positions along thetrough conveyor of the fold bars and the pull rolls can be adjusted.Preferably, the guide sheets are sheets of thin plastic material, e.g.polyethylene.

6 Claims, 4 Drawing Figures PATENTEDHAYZI m4 sum 1 OF 2 OTHERAPPLICATIONS The present application is a continuation-in-part of ourco-pending application Ser. No. 719,957 filed Apr. 9, 1968 and nowabandoned.

FIELD OF INVENTION This invention relates to methods meric foam slabs.

BACKGROUND for producing poly- A well-known and generally employed meansof constructing the required trough conveyor is to arrange a pair ofrigid side walls in parallel spaced relationship above, but close to, anendless belt conveyor. The belt conveyor and the rigid side walls arethen lined with, for example, waxed-paper sheets drawn from supply rollsso that the sheets (sometimes a single sheet is used folded upwardly ateach side) constitute a continuous open-topped trough of rectangularcross-section which is transported by the belt and slides past the rigidside walls. Such an arrangement of paper sheets (or a single foldedsheet) can be considered as, per se, constituting a continuous troughconveyor. Such an arrangement is well-known but details of one specificarrangement can be found in U.S. Pat. No. 3,152,361 (Edwards).

After the foaming action has-ceased the resultant continuous slab offoam material, which may have for example a cross-section two metreswide and one metre high, continues down the conveyor to undergo a curingprocess and is then cross-sawn into blocks of convenient length. Thus,for as long as the mixture of liquid foam reactantsis poured onto theupstream end of the trough conveyor, a slab of cured foam materialpasses out of the downstream end of the conveyor. With such ahigh-output continuous process, utilizing relatively expensive startingmaterials, it is essential that the resultant foam product is of aconsistently high quality; in particular that it is free from anysurface deformities such as splits and tears and also that the densityof the foam is maintained as near uniform as possible.

In order toachieve uniform density of the product, it is essential thatthe mixture of liquid foam reactants should be free to rise naturally,due to the chemical reaction, without any inhibiting influences. Thus,the aforementioned trough conveyor must be open-topped and the risingfoam must not encounter any kind of shaping or limiting means such as adoctor blade or top cover of the trough. However, as is well-known tothose informed in the subject art, friction or adhesion occurs betweenthe rising foam and the paper side wallsof the trough conveyor resultingin a product which has a convex top surface (as seen in cross-section).

In the subsequent conversion of a foam block (to mattresses or whatever)the ideal cross-sectional shape of the block is rectangular, for maximumeconomical utilization of the block material. Thus, various proposalshave been made for avoiding or overcoming the aforementioned friction oradhesion in an attempt to produce a block which has a flat top and istruly rectangular in section; see for example, U.S. Pat. Nos. 3,123,856(Dye et al.) and 3,325,823 (Boon).

However, the only proposal which so far has found A wide acceptanceinvolves the introduction of an additional sheet or web of materialbetween the rising foam and the paper side walls of the continuoustrough conveyor, as first disclosed in U.S. Pat. No. 3,091,811 toHackert. Such additional sheets are to be moved in a direction and at aspeed such that the horizontal component equals that of the conveyedfoam and the vertical component is the same as the rising speed of thefoam top surface. In other words, said additional sheets are moved alongupwardly inclined paths so that no friction (no movement) occurs betweenthe upper'regions of the sides of the rising foam and said sheets.

We have sought to provide a method for the continuous production of aslab of polymeric foam which is adapted to the requirements ofmass-production factory conditions. As previously mentioned, thereactants constituting the starting materials for such production arerelatively expensive so thatwastage is unacceptable. Also, in spite ofthe conditions of continuous mass production, the resultant foam strandsmust be free of tears or splits at the surfaces, must have asubstantially uniform density, and must have a cross-sectional shapewhich is, as closely as possible, rectangular. Furthermore, such aconsistent result must be achieved.

In achieving a rectangular cross-section, it is not, of course,acceptable to employ means which create some other unacceptablecharacteristic in the resultant product. For example, we are aware of aprior proposal to introduce very narrow belts of material between theside walls of the trough conveyor and the foam, the belts being locatedonly adjacent the top surface of the foam. However, such proposal is noteffective in that it necessitates a top cover for the trough conveyor,which inevitably results in foam of non-uniform density.

Our investigations have shown that it is necessary to provide someadjustment, preferably continuous, of the means controlling the path oftravel of the additional intervening sheet or web. The position alongthe trough conveyor at which the liquid foam reactants will start torise (expand) cannot be predetermined as between successive batches. ofsimilar reactants and certainly not as between different successivebatches of reactants, as for example when a foam of one resiliency is tobe followed by a foam of a different resiliency. Similarly, the rate ofrise (or expansion) of the foam cannot be predetermined with accuracy.Consequently, adjustment facilities must be provided to insure that theadditional intervening sheet or web (hereinafter referred to as theguide sheet) can be located and moved in accurate registration with theside of the foam. F urthermore, the conditions of continuous massproduction require that the method and apparatus for achieving thesedesiderata shall be as simple and reliable as possible.

SUMMARY OF INVENTION A primary object of the present invention is to prosheets between the rising foam and the side walls of a trough in whichthe foam is being cured, which method is sufficiently simple so thatcontinuous adjustment of the path of travel of each said guide sheet isfacilitated to the extent that acceptable flat-topped foam slabs can beproduced continuously in any reasonable and normal circumstances with aminimum of skill or expertise on the part of the operator.

A further object is to provide that each guide sheet shall be passedaround a respective straight fold bar prior to functioning to controlthe shape of the foam.

Another object is to provide that said guide sheets shall be thin sheetsof plastic material, preferably polyethylene.

An additional object is to provide automatic control means to controlthe location of each respective fold bar.

A further object is to provide that each said guide sheet shall be movedaround its respective fold bar by pull rolls the alignment of which,relative to said guide sheet, is controlled automatically.

These and other objects of the invention are achieved in a method ofproducing a slab of polymeric foam in a continuous open-topped troughconveyor wherein an initially-liquid mixture of foam reactants ispermitted to foam freely in a mobile conveyor trough as the trough movesalong and guide sheets are introduced between the rising foam and the,trough sides in order to prevent friction between the foam and thetrough sides. In accordance with the invention, there is provided animprovement comprising introducing each guide sheet downwardly into thetrough adjacent the region where foaming begins, folding the guide sheetaround a fold bar having an attitude such that the guide sheet isthereby directed along an upwardly-inclined path corresponding to therising level of the foam, and advancing the guide sheet along said pathtogether with and in contact with the foam. As a result of thisimprovement, the resultant foam slab is produced with a substantiallyflat top surface.

In apparatus for producing a slab of polymeric foam in a continuousopen-topped trough conveyor, an initially-liquid mixture of foamreactants is permitted to foam freely in the conveyor trough as thetrough moves along, and guide sheets are introduced between the risingfoam and the trough sides in order to prevent friction between the foamand the trough sides. In this apparatus is provided an improvementcomprising, at

each side of the trough guide, sheet supply means located adjacent theregion where foaming begins, a fold bar located in the trough below saidsupply means and in an attitude such that, when the guide sheet is introduced downwardly into the trough and folded around said fold bar, theguide sheet will thereafter be directed along an upwardly-inclined pathcorresponding to the rising level of the foam, and means for advancingthe guide sheet along said path together with and in contact with thefoam whereby the resultant foam strand will be produced with asubstantially flat top surface.

Other objects and advantages of the present invention will becomeapparent from the following detailed description and by reference to theaccompanying drawings. It should be understood, however, that thedetailed description and examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invenguide sheet on its tion will become apparent as the descriptionherein progresses.

BRIEF DESCRIPTION OF DRAWING Reference is now made to the accompanyingdrawings which form a part hereof, wherein:

FIG. 1 is a diagrammatic perspective view of apparatus in accordancewith the present invention, the nearest side being partially brokenaway;

FIG. 2 is a side elevational section along the longitudinal center lineof FIG. 11 showing some details not given in FIG. 1 but omitting thefoam;

FIG. 3 is a detail as seen in the direction of arrow A in FIG. 2; and

FIG. 4 is a detail as seen in the direction of arrow B in FIG. 2.

DETAILED DESCRIPTION OF INVENTION The apparatus shown in FIG. 1comprises a pair of parallel spaced rigid side walls I located instationary relation above but close to an endless conveyor belt 2. Apaper trough conveyor comprises a base 3 and side walls 4, the papersheets constituting the trough being drawn continuously from supplyrolls (not shown) and being longitudinally transported by and with thebelt 2 from the left to right as seen in the drawing. A mixture 5 ofliquid foam reactants is deposited on the bottom of the trough conveyorfrom a nozzle 6 feeding from a mixing head (not shown). The nozzle isreciprocated, as indicated by arrows, across the trough conveyor inorder to deposit an even layer of foam reactants onto the bottom of theconveyor. Although some reaction takes place initially, the foamreactants perceptibly start to expand and rise at what is termed thecream line indicated by chain line 7. Thereafter, the top surface of thefoam rises due to chemical reaction until the foam reaches a conditionof maximum expansion; that is the point of full rise indicated by thechain line 8. Thereafter, the fully expanded foam slab (seen in sectionat 5a) continues along the trough conveyor to a position (not shown)where it is fully cured and subsequently cross-sawn into utilizablelengths.

In the foaming region, that is the region of the trough conveyor betweenthe lines 7 and 8, is located a supply roll 10 of material constitutinga guide sheet 111. An example of a suitable material is polyethylenesheet of about 0.06 mm. thickness, having a specific weight of 0.918 anda melt index of from 1.5 to 2.0. (The melt index of polyethylene is theweight in grams of material pressed through a circular orifice of 2.1mm. diameter by a weight of 2.1 kilograms at a temperature of C during aperiod of 10 minutes). Also provided is a folding bar 12 and pull rolls13. The folding bar 12 is supported and controlled from a mechanismindicated at 14 and the pull roll 13 is supported and controlled from amechanism indicated at 15. The details of the mechanisms 14 and 15 willbe illustrated and explained hereinafter. The guide sheet 14 isintroduced in a vertical direction into the trough conveyor and isfolded around the folding bar 12 from which it extends along anupwardlyinclined path through the foaming region to pull rolls 13, therolls engaging the upper edge of the sheet 11. Although not shown, asimilar arrangement is also provided on the opposite side of the troughconveyor.

The surface speed of the pull rolls 13 is related to the speed of theconveyor belt 2. The pull rolls 113 pull sheet 11, from the supply roll10., around the folding bar 12 and thereafter along a path which is madeto correspond to the top surface 5b of the expanding foam 5. The path ofthe guide sheet 11 will depend upon the respective attitudes, andpositions along the trough conveyor, of the folding bar 12 and the pullrolls 13, as will be explained hereinafter.

When the guide sheet 11 has passed through the pull rolls 13, the partof the sheet extending above the top surface of the fully-expanded foamis allowed to fall limply over the top of the foam, as indicated at 11a.Thus the guide sheet, after rising with the foam until the end of thefoaming region, thereafter remains in contact with the fully-expandedfoam until the foam has cured sufficiently to permit the guide sheet tobe removed without damaging the foam surface.

In FIG. 2, it is additionally seen that the mechanism 14 comprises asaddle-unit 20 movable by means of a hand wheel 21 along a rack 22attached to the top of the rigid side wall 1. The fold bar 12 ispivotally attached at 23 to the unit 20 and is pivotally adjustable bymeans of an arm 24 which can be reciprocated by a motor 25.

The mechanism comprises a saddle-unit 30 movable by means of a handwheel 31 along a rack 32 attachedto the top of the rigid side wall 1.The pull rolls 13 form'part of an assembly which is pivotally attached 1at 33 to the shaft of a positional motor 34 and the rolls 13 are rotatedthrough a flexible drive 35 by a motor 36. a

Thus, the saddle-units 20 and 30 can be positioned independently alongthe trough conveyor; the attitude of fold bar. 12 can be adjustedthrough appropriate energization of motor 25; and the attitude of pullrolls 13 can be correspondingly adjusted (as indicated by arrows)byappropriate energization of motor 34. Consequently, theupwardly-inclined path of travel of the guide sheet 11 can becontinuously controlled to insure accurate registration between theguide sheet and the contiguous foam notwithstanding alteration of theposition where foaming commences or the rate of rise of the foam. Thedegree of accuracy achieved in maintaining registration between thesheet and the foam will, of course, depend upon the skill and experienceof the operatives concerned. It should be noted that the hand wheels 21and 31 can be replaced by motors in order to achieve maximum automationof the apparatus. Also, the motors 25 and 34 can be replaced by handwheels if a greater degree of manual control is de sired.

Referring to the fold bar 12, the guide sheet 11 will exhibit a tendencyi0 drift along the fold bar (to the right as seen in FIG. 2). Theinvention provides for automatic correction of this tendency through apair of idler rolls whose rotational axes are set at a small advancedangle (e.g. 10) relative to the perpendicular to the normal direction oftravel of the guide sheet If. The rolls 40 are normally held out ofcontact with the guide sheet 11, by virtue of the edge of the guidesheet interrupting a flow of air from a port 41 (see also FIG. 3). Anytendency of the guide sheet to run off the fold bar 12 moves the guidesheet to the right (as seen in FIG. 2) so as to uncover the port 41.This allows air to flow to a port 42 and actuate a diaphragm 43 whichmoves the rolls 40 together to pinch the guide sheet.

Thenceforth the guide sheet tends to travel in a direction perpendicularto the axes of rolls 40. This corrects the position of the guide sheeton the fold bar 12 until the edge of the guide sheet again interruptsthe air cir cuit to release the rolls 40.

Referring to the pull rolls 13, it is desirable that the upper edge ofthe guide sheet 11 shall pass between the pull rolls at a predeterminedlocation along the axes of the pull rolls. The actual location of saidupper edge will vary in dependence upon the angle of the pull rollsrelative to the direction of said upper edge of the guide sheet. Theinvention provides for automatic adjustment of the location of the upperedge of the guide sheet by providing two air ports 50 and 51 (see alsoFIG. i) connected to an air supply. When the guide sheet is correctlylocated, its upper edge. covers the port 51 but does not cover the port50. In this condition airactuated switches 52 and 53, connected in theenergization circuit of motor 34, are open and the motor is stationary.If the sheet 11 rises, the air supply to switch 52 is cut off and theswitch operates to drive the shaft of motor 34 clockwise. The pull rolls13 are thus pivoted so that the sheet 11 moves down to its normalposition. If the sheet moves down sufficiently to uncover the port 50,air is supplied to switch 53 which operates to drive the shaft of motor34 counter-clockwise so that the guide sheet 11 is raised to it normalposition.

EXAMPLE I parts by weight Polyether Triol (Polypropylene Glycol) (UnionCarbide Polyol L-56) 100.00 Water 3.20 Triethylenc Diamine (DABCO) 0.10Silicon Surfactant (Union Carbide L-540) 1.50 Stannous Octoate-Catalyst(T-9) 0.20 Toluene di-Isocyanate (Index I05) 42.00

As-the mixture commenced foaming from an observed cream-line 7, a guidesheet 11 of polyethylene of thickness 0.06 mm., specific weight 0.918and melt index 1.8, was drawn downwardly at each side of the troughconveyor and folded about a respective fold bar 12 so that each sheetthereafter was transported along an upwardly inclined path.Transportation of the sheets was effected by respective pull rolls 13and, after passing through the pull rolls, the part of each sheetextending above the surface of the expanded foam was allowed to fallfreely on the foam surface. At each side of the conveyor, the respectivehand wheel 21 was operated to position the fold bar 12 and guide sheet11 about 2 meters downstream from the cream-line 7.

, Similarly the respective hand wheel 31 was operated to position thepull rolls 13 about 1 meter upstream from the full-rise line 8. Eachmotor 25 was then operated to adjust the attitude of its fold bar 12 andeach motor 34 was operated to adjust the attitude of its pull rolls 13so that the respective guide sheets 11 moved in accurate registrationwith the rising top surface of the foam.

The rising foam was kept under observation and any alteration of thepath followed by the top surface of rising foam was compensated for bycorresponding alteration of the paths of the guide sheet 11, byadjustment of the appropriate one or more of the aforementionedcontrols.

in order to check the registration between a guide sheet 11 and the topsurface of the foam, an ink marking pen was applied to thedownwardly-moving polyethylene sheet ss as to produce a straight inkline extending along the upwardly-inclined sheet just above the foam topsurface. Appropriate adjustments were then made to the apparatus toinsure that the ink line extended parallel to the foam top surface.

After the expanded foam had cured sufficiently, the polyethylene sheetswere removed from the foam together with the paper sheets constitutingthe trough conveyor. Due to the action of the polythene sheets, 15 theresultant foam slab had a rectangular cross-section. Furthermore, thefoam was free of any surface splits or tears and the density throughoutthe foam was uniform.

2 EXAMPLE u 0 in order to produce a slab of polyester flexible foam, thesteps of Example I were carried out with a mixture of foam reactantsconsisting of:

' parts by weight A polyester of adipic acid, di-ethylene glycol 100.00and a triol (e.g. glycol), said polyester having a hydroxyl number ofabout 56 and an acid number of about I Mixture of 80% 2-4, toluenediisocyanute 49.00 and 20% 2-6, toluene diisocyanate Water 3.5 Methylammonium oleate 0.80 Sulphonated castor oil 1.7 A tertiary amine type DB(di butyl benzyl 0.5 amine) N-coco-morpholine 0.65 N-ethyl-morpholine2.]

EXAMPLE Hi In order to produce a slab of polyether rigid foam, the stepsof Example I were carried out with a mixture of foam reactantsconsisting of:

parts by weight Polypropylene ether, hydroxyl number l00.00 about 490Mixture of 80% 2-4. toluene diisocyanate 65.00 and 20% toluenediisocyanate N,N,N',N'tctra methyl 1,3 butane diamine 0.75 Silicone oil1 0.6 Trichlorofluoromethane 30.00

Modifications of the aforedescribed embodiment are possible within thespirit and scope of the appended claims. For example, the material ofthe guide sheets if might be felt or paper instead of a plasticsmaterial. The guide sheets could be introduced into the trough conveyornot vertically but at an angle to the vertical direction. Insofar asboth sides of the rising foam are likely to behave in the same way, thecorresponding ad ustment controls on each side of the trough conveyormight be linked so that adjustment of a control on one 6 side of theconveyor will also produce adjustment of the corresponding control onthe other side of the conveyor. Furthermore, the automatic controlarrangements described with reference to FIGS. 3 and 4 might includephotoelectric sensors rather than the described pneumatic sensors.

What is claimed is:

1. In a method of producing a slab of polymeric foam in a continuousopen-topped trough conveyor wherein an initially-liquid foamablepolyurethane reaction mixture is permitted to foam freely betweenregions whereat foaming is effectively initiated and completed in alongitudinally moving conveyor trough and guide sheets are introducedbetween the rising foam and the trough sides in order to preventfriction between the foam and the trough sides, the improvementcomprising introducing each guide sheet downwardly into the troughthrough the open top thereof towards its bottom at a location adjacentthe region where foaming begins, folding the guide sheet around a foldbar having an attitude such that the guide sheet is thereby directedalong an upwardly-inclined path corresponding to the rising level of thefoam, advancing the guide sheet along said path together with and incontact with the foam, ad justing the attitude of said fold bar tomaintain the upward ly-inclined path of the guide sheet incorrespondence with the rising level of the foam, and keeping the guidesheet in contact with the foam after the foam leaves the foaming region,whereby a foam slab is produced with a substantially flat top surface.

2. The improvement as claimed in claim it, comprising engaging the upperedge of the guide sheet with pull rolls positioned adjacent the regionwhere foaming is completed and adjusting the attitude of said pull rollsrelative to the guide sheet in dependence upon the attitude of said foldbar.

3. The improvement as claimed in claim 1, comprising engaging theupper-edge of the guide sheet with pull rolls positioned adjacent theregion where foaming is completed and adjusting the location along thetrough conveyor of said fold bar and said pull rolls to compensate forshifting of the regions where foaming begins and ceases.

4. The improvement as claimed in claim ll, comprising sensing deviationof the guide sheet, from its downward path of travel and returning theguide sheet to its original path in response to such sensed deviation.

5. The improvement as claimed in claim 1, comprising engaging the upperedge of the guide sheet with pull rolls positioned adjacent the regionwhere foaming ceases, sensing deviation of said upper edge from saidupwardly inclined path of travel, and returning the guide sheet edge tosaid upwardly inclined path of travel in response to such senseddeviation by adjusting the angular relationship between said guide sheetedge and the rotational axes of said pull rolls.

6. The improvement as claimed in claim 1 wherein said guide sheet isintroduced downwardly into the trough at a location downstream of theregion where

2. The improvement as claimed in claim 1, comprising engaging the upperedge of the guide sheet with pull rolls positioned adjacent the regionwhere foaming is completed and adjusting the attitude of said pull rollsrelative to the guide sheet in dependence upon the attitude of said foldbar.
 3. The improvement as claimed in claim 1, comprising engaging theupper edge of the guide sheet with pull rolls positioned adjacent theregion where foaming is completed and adjusting the location along thetrough conveyor of said fold bar and said pull rolls to compensate forshifting of the regions where foaming begins and ceases.
 4. Theimprovement as claimed in claim 1, comprising sensing deviation of theguide sheet, from its downward path of travel and returning the guidesheet to its original path in response to such sensed deviation.
 5. Theimprovement as claimed in claim 1, comprising engaging the upper edge ofthe guide sheet with pull rolls positioned adjacent the region wherefoaming ceases, sensing deviation of said upper edge from said upwardlyinclined path of travel, and returning the guide sheet edge to saidupwardly inclined path of travel in response to such sensed deviation byadjusting the angular relationship between said guide sheet edge and therotational axes of said pull rolls.
 6. The improvement as claimed inclaim 1 wherein said guide sheet is introduced downwardly into thetrough at a location downstream of the region where foaming begins.